The Mind Snatchers (1972)

Synopsis
Based on the long-running Broadway play by Dennis Reardon, The Happiness Cage, a multinational filmmaking effort, is a drama about medical experimentation in the U.S. military. The experiment is a brain operation which removes pain, replacing it either with bliss or sensual satisfaction. It is at first attempted on terminal cancer patients, but finally the doctors receive permission to test the procedure on a healthy but thoroughly obnoxious subject (Christopher Walken). ~ Clarke Fountain, All Movie Guide